Illumination systems having a light source and a beam-control element are well known in the art. They are used, inter alia, in spotlights, flashlights, vehicle headlights, shop lights and office lights. Beam control is often required to increase or decrease the degree of collimation of the illumination system. For example, when illuminating an item which is located relatively nearby, less collimation is required compared to items located further away. Also the intensity of the light illuminating an item may be adapted by adapting the degree of collimation of the illumination system.
An illumination system having a light source and means for controlling the degree of collimation of the emitted light is, for example, known from U.S. Pat. No. 4,951,183. In this US patent, a flashlight with a variable light beam is disclosed, which includes a tube with a head provided at a front end. A light reflector is disposed in a front end of the head. A casing is force-fitted within the front end of the tube. A switch is fixed on the casing. An end cap, a spring and an end plate are disposed in an insulator which is received in a retainer. A light bulb is retained in the retainer. The switch controls an electrical circuit of the flashlight. The light bulb is stable relative to the tube, so that a rotation of the head relative to the tube makes the light reflector move relative to the light bulb. Due to this moving of the light bulb relative to the light reflector, the width of the light beam emitted by the flashlight is altered.
A drawback of this flashlight is that a relatively large movement of the light reflector relative to the light bulb is required to alter the width of the light beam emitted from the flashlight.